Flat Roof and Solar Energy Design
Few homes are designed with a flat or marginally sloped roof, although many business facilities including retail have a flat roof. The term flat doesn’t mean perfectly horizontal, and generally the roof surfaces are built with minor angles to make drainage more effective. Some may slope slightly in one direction. Others may have a more complex set of minor sloped surfaces for drainage. For the purposes of solar energy system design, they are all considered flat.
Designing for a Flat Roof
For larger solar energy systems, often 100 kW and greater, economies of scale apply that can reduce the total cost for each unit of solar power produced. Longer strings and rows of solar panels may be installed. Larger capacity power inverters could be applied to these larger arrays, resulting in fewer over components.
In Massachusetts and Rhode Island, most flat roof structures allow for more solar panel mounting options. One of the most preferred methods is a ballasted mounting, where the solar panels and racking are interconnected and weighted to stay in contact with the roof. No direct mechanical fastening is required. Mechanical fastening and a combination of mechanical and interconnect fastening is used where needed, too.
With direct mechanical fastening, smaller sections of solar panels and racking can be independently affixed to the roof support structure. A hybrid version allows for more interconnection of solar arrays similar to a ballasted system, with few attachments to the roof supports.